N-(Phosphonomethyl)glycine, also known by its common name glyphosate, is a widely-used broad spectrum post-emergent herbicide used to control the growth and proliferation of undesired plants. Typically it is applied to the foliage of the target plant, whereafter it is absorbed by the foliar tissue and translocated throughout the plant. Glyphosate is conventionally applied as an aqueous composition of a more water soluble salt form thereof. Commercially available formulations of glyphosate contain glyphosate in the form of any of its agriculturally acceptable salt in aqueous solution. However, the range of N-(Phosphonomethyl)glycine salts useful for controlling weeds is very broad (J. E. Franz et al., Glyphosate: A Unique Global Herbicide, ACS Monograph 189, American Chemical Society, Washington, D.C., 1997, pp. 27-64, herein incorporated by reference). However, glyphosate free acid form per se is relatively insoluble in water, it is usually formulated as any of its water soluble salt.
The article entitled “A unique formulation of glyphosate in the acid form”, Volgas G, Roberts J, Wayland M and Alford B, Journal of ASTM International, Volume 5, Issue 4 relates to a formulation comprising glyphosate acid. This article teaches a disadvantage associated with these known glyphosate-salt formulations is that they need substantial amount of surfactants to enhance their uptake. It has been believed that the formulations including glyphosate free acid form would not need to rely on reduced surface tension or other surfactant effects to provide excellent uptake and herbicide efficacy. For example, in known 41 SL formulations of glyphosate isopropylamine salt, about 15% or more of amine ethoxylate surfactants are used, which is clearly undesirable.
Moreover, it has been found by the present inventors that the known formulations comprising glyphosate salt in combination with other active ingredients suffer from very poor suspensibility and are known to often fail the wet sieve test. These products display a considerable amount of sedimentation with time, often forming hard rock type lumps at the bottom of the storage containers. The increased sedimentation further aggravates the problem of nozzle clogging during the spraying application by a farmer. It is observed that when such a formulation is prepared as a diluted liquid or a solution to be sprayed, the same does not remain sprayable after the passage of a certain amount of time because of the high insoluble content. This can sometimes lead to a farmer rejecting an otherwise good product, which is certainly undesirable.
The present inventors attempted mixing an existing pendimethalin 40 SC formulation with a 41% glyphosate isopropylamine salt SL formulation in a 1:1 ratio to obtain a 20:20 product. This pre-mix displayed a suspensibility of 23% and heavy retention of particles on 500 BSS sieve. It was concluded that glyphosate salt would be mutually incompatible with other dinitroaniline herbicides as well apart from pendimethalin, such as oryzalin.
It was further found that the formulations hitherto known in the art comprising a glyphosate salt with oryzalin were retained by about 30-50% on a wet screen #150. It is thus desirable to develop a suspension concentrate formulation comprising glyphosate in a suitable form, wherein the formulation solves the problem of clogging associated with the conventional formulation and preferably, displays at most from about 0% to about 10% retention on standard wet sieve analysis.
Further, most of the known processes for the preparation of glyphosate which are described in the literature involve the separation of glyphosate in its acid form, which is converted to a desired salt form prior to being formulated. Accordingly, a formulation that includes glyphosate in its acid form would eliminate the need for it to be converted to its desired salt form prior to being formulated, which is desirable.
A formulation comprising glyphosate acid is mentioned in BCPC Monogram No. 28, 1985, by D J Turner and P M Tabbush. However, this disclosure teaches heating the glyphosate acid at 100° C. for about an hour with an excess of a fatty amine in water, during which process the glyphosate acid present in the formulation is converted to its salt form.
EP 206,537 describes a solid formulation comprising glyphosate derivatives. This formulation is taught to be prepared by melting a surfactant and adding the glyphosate compound in a solvent to the concentrated solution. The solvent is thereafter removed. However, this publication does not exemplify a formulation comprising glyphosate free acid.
U.S. Pat. No. 5,118,338 describes a water soluble powdery or granular free flowing formulation comprising glyphosate free acid and a specified surfactant. However, the solid formulations are known to have some inherent disadvantages. It is often desirable to present a herbicide in a concentrate form, which may be mixed with water before spray to form an emulsion spray. Moreover, it is also desirable to present a formulation having a high herbicide component, which is not always possible with a solid formulation.
It is known that suspension concentrate formulation provide these benefits as it comprises a water-based particulate suspension which contains no solvent. The microscopic particles of the herbicide remain on the applied surface for easy penetration and the lack of a solvent ensures no staining or odor problems.
It is therefore desirable to present a suspension concentrate formulation comprising glyphosate in its free acid form thereby overcoming the need to incorporate substantial amount of surfactants without compromising the herbicidal efficacy of the formulation.
Certain sulfanilamides are known selective pre-emergence herbicides, effective against many weeds. One such sulfanilamide is 4-(dipropylamino)-3,5-dinitrobenzenesulfonamide, commonly known as oryzalin. Oryzalin is a selective preemergence surface-applied herbicide used for control of annual grasses and broadleaf weeds in fruit trees, nut trees, vineyards, established bermudagrass turf and established ornamentals.
British Patent Specification No. 2,131,327 disclosed spray equipment useful for rotary dispensation of herbicides. Difficulties are encountered in obtaining a uniform spray when known spray mixtures of N-phosphonomethyglycine and sulfanilamide herbicides are employed using a device designed to discharge a herbicidal mixture from a distribution element by centrifugal force.
PCT application, WO 1997/031535 A1, discloses a synergistic combination of N-phosphonomethylglycine ester or acid adduct of an ester and oryzalin.
European patent, EP0376910 discloses an herbicidal aqueous composition comprising N-phosphonomethyglycine, a sulfanilamide herbicide and a polymeric thickening agent in an amount sufficient to thicken the composition such that at 25° C. the time elapsed for 100 ml of the composition to pass through the measurement orifice of a Ford B2 Cup is in the range of about 20-150 seconds. The composition was delivered to a target area using the rotary spray device disclosed in British Patent Specification No. 2,131,327. The experimental procedures exemplified in EP'910 were attempted by the present inventors. It was found that the resultant formulations demonstrated poor suspensibility (%) and failed the wet sieve test. Consequently, nozzle choking during the spray application was also observed. Moreover, none of the examples teach a suspension concentrate formulation including glyphosate in its free acid form. It is further often seen that for active ingredients that are formulated as suspension concentrates and which are denser than water tend to settle in the packaged product, which is undesirable.
It has thus been found that when glyphosate isopropylammonium salt is combined with oryzalin, it causes instant sedimentation and thus makes it unsuitable for spray application as the physical system loses its homogeneity and it blocks the spray nozzle. Another disadvantage of formulations comprising glyphosate in its salt form is the need to use a higher amount of surfactant, which is clearly undesirable.
PCT Publication No. WO 03/026429, which is incorporated herein by reference in its entirety, discloses compositions comprising suspension concentrates containing glyphosate acid and methods of preparing such suspension concentrates. However, this publication does not contemplate combination of glyphosate acid with other herbicides, particularly with dinitroaniline herbicides and more particularly with oryzalin. This publication therefore does not contemplate the problem of mutual physical incompatibility between glyphosate and oryzalin, which the present invention sets out to solve.
It is thus desirable to present a storage stable suspension concentrate formulation comprising a combination of glyphosate in its free acid form in addition to oryzalin, which is an unmet need in the art.